TW202235938A - Mitigation of polarization impairments in optical fiber link - Google Patents

Abstract

An optical data communication system includes an optical transmitter and an optical receiver. A polarization-maintaining optical data communication link extends from an optical output of the optical transmitter to an optical input of the optical receiver. The polarization-maintaining optical data communication link includes at least two sections of polarization-maintaining optical fiber optically connected through an optical connector. The at least two sections of polarization-maintaining optical fiber have different lengths. The optical connector is configured to optically align a fast polarization axis of a first polarization-maintaining optical fiber to a slow polarization axis of a second polarization-maintaining optical fiber. The optical connector is also configured to optically align a slow polarization axis of the first polarization-maintaining optical fiber to a fast polarization axis of the second polarization-maintaining optical fiber.

Description

Mitigation of Polarization Loss in Optical Fiber Links

This invention relates to optical data communication.

Optical data communication systems operate by modulating laser light to encode digital data patterns. The modulated laser light is transmitted from the sending node to the receiving node via the optical data network. The modulated laser light that has reached the receiving node is reverse modulated to obtain the original digital data pattern. Therefore, the implementation and operation of optical data communication systems depend on having reliable and efficient means for modulating and receiving optical signals.

The vast majority of fiber optic communication links use non-polarization-maintaining fibers. Typical components (e.g., optical fibers, optical detectors) that make up commercial fiber optic communication systems are sufficiently polarization insensitive to provide efficient data communication while enabling random changes in polarization in fiber optic links without controlled. However, certain integrating optics can more efficiently process light received via an optical fiber when the polarization of the light in the optical fiber is controlled. It is against this background that the present invention was produced.

In an exemplary embodiment, an optical data communication system is disclosed. The optical data communication system includes an optical transmitter, an optical receiver, and a polarization maintaining optical data communication link extending from an optical output of the optical transmitter to an optical input of the optical receiver. The polarization maintaining optical data communication link includes at least two sections of polarization maintaining optical fiber optically connected by an optical connector. The at least two sections of the polarization maintaining fiber have different lengths.

In an exemplary embodiment, an optical data communication system is disclosed. The optical data communication system comprises a polarization maintaining optical data communication link comprising a first polarization maintaining optical fiber optically coupled to a second polarization maintaining optical fiber such that aligning a fast polarization axis of the first polarization maintaining fiber with a slow polarization axis of the second polarization maintaining fiber, and a slow polarization axis of the first polarization maintaining fiber The polarization axis is aligned with a fast polarization axis of the second polarization maintaining fiber.

In an exemplary embodiment, a method for operating an optical data communication system is disclosed. The method includes transmitting a plurality of optical signals from an output of an optical transmitter to an optical input of an optical receiver via a polarization maintaining optical data communication link, wherein the polarization maintaining optical data communication link comprises At least two sections of polarization maintaining optical fiber are optically connected via an optical connector. The at least two sections of the polarization maintaining fiber have different lengths.

In an exemplary embodiment, a method for operating an optical data communication system is disclosed. The method includes transmitting a plurality of optical signals over a polarization maintaining optical data communication link comprising a first polarization maintaining optical fiber optically coupled to a second polarization maintaining optical fiber . The first polarization maintaining fiber is optically coupled to the second polarization maintaining fiber such that a fast polarization axis of the first polarization maintaining fiber is aligned with one of the second polarization maintaining fibers Slow polarization axes are aligned, and a slow polarization axis of the first polarization maintaining fiber is aligned with a fast polarization axis of the second polarization maintaining fiber.

Other aspects and advantages of the present invention will become clearer from the following detailed description and accompanying drawings exemplified by examples of the present invention.

In the following description, specific details are set forth in order to provide a thorough understanding of embodiments of the invention. However, one skilled in the art will be able to practice the present invention without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Optical data communication systems operate by modulating laser light to encode digital data patterns in the electrical domain into modulated optical signals in the optical domain. The modulated optical signal is transmitted through an optical fiber to an optoelectronic receiver where it is detected and decoded to obtain the original encoded digital data pattern back in the electrical domain. In many optical data communication systems, the polarization state of the light in the optical fiber is not controlled, and the operation of the system may be disturbed by small movements of the optical fiber and/or changes in the ambient temperature. In these systems, integrated optical devices, such as optoelectronic receivers in particular, must process incoming optical signals with arbitrary polarization variations over time. Thus in certain embodiments it is desirable to use polarization maintaining (PM) optical links such as optical fibers, light guides, etc. to interface with such integrated optics. In an ideal PM optical link for data communication, only a single polarization of light is excited to avoid loss of this single polarization of light by and/or associated with another polarization of light. However, in practical optical data communication systems, fiber optic sections usually need to be connected and these connections are not optically perfect, thus causing cross-coupling between the two polarizations.

In PM optical data communication links, cross-coupling between polarizations can lead to optical transmission losses, especially losses and multipath interference that do not exist in non-PM optical data communication links. Embodiments described herein for mitigating and/or managing polarization-related impairments in optical transmission over PM optical data communication links include one or more of the following: insertion and use of polarization devices, management of polarization mode dispersion (eg, by selecting fiber type, fiber length, and/or coupling selected fibers in opposite orientations), and managing cross-coupling between polarizations (eg, by selecting optical connectors and/or fiber splices).

In some embodiments, the first integrated optics device transmits a polarized optical signal into a PM optical data communication link that optically connects the first integrated optics device to the second integrated optics device . The polarized optical signal travels through the PM optical data communication link and is received by the second integrated optical device. When the polarized optical signal travels through the PM optical data communication link between the first integrated optical device and the second integrated optical device, the polarized optical signal passes through multiple polarization paths and experiences multipath interference (MPI). In various embodiments, the MPI is a function of one or more properties of the PM optical data communication link, such properties including one or more of the following: properties of the PM fiber section within the PM optical data communication link (especially For example, the length of the PM fiber section, the group index, the thermal coefficient of the PM fiber section), the characteristics of the optical connector between the PM fibers in the PM optical data communication link (such as the failure of the optical connector and/or splice alignment angle and/or cross-coupling), the alignment between the PM fiber and the first integrated optics device, and the alignment between the PM fiber and the second integrated optics device.

When the optical data communication system includes an integrated optical transmitter operable to transmit a plurality of optical signals modulated by high bandwidth modulation to each of several wavelength division multiplexed (WDM) wavelengths, we are particularly concerned about avoiding via Polarization-dependent impairments in optical transmission of PM optical data communication links. We are also particularly concerned about avoiding in-transmission of light over PM optical data communication links when the optical data communication system includes an integrated optical receiver operable to detect light incident from only a single polarization of the PM fiber polarization. Polarization-related impairments. We are also particularly concerned about avoiding the transmission via PM optics when the optical data communication system does not provide substantial adjustment/control of the optical wavelength of the transmitted modulated optical signal in response to, inter alia, the spectrum of optically transmitted wavelengths observed during operation of the optical data communication system. Polarization-related impairments in optical transmission of data communication links.

The challenges associated with polarization-related impairments of optical transmission over PM optical data communication links are especially acute for baud rates greater than about 20 Gsamples per second, and for baud rates greater than about 45 Gsamples per second. The challenges associated with such impairments are even more severe at such optical data rates, since polarization-related impairments intersect with signal bands in the frequency domain with a higher probability at these optical data transmission speeds. Also, as the number of data communication wavelength channels per optical fiber increases, the chance that at least one data communication wavelength channel experiences unacceptable polarization-dependent impairments increases. Also, as the number of optical fibers attached to each of the integrated optical transmitter and/or integrated optical receiver increases, the chance that at least one data communication wavelength channel experiences unacceptable polarization-dependent impairments increases.

For example, integrated optics connected to transmitters and/or receivers operating with a small number of optical fibers (e.g., less than four optical fibers) and/or with a small number of WDM channels per optical fiber (e.g., fewer than five WDM channels per optical fiber), may Can suffer from moderate yield loss due to polarization-related impairments in light transmission. However, an optical data communication system that includes many optical fibers (such as four or more optical fibers) and/or each optical fiber has many WDM channels (such as five or more WDM channels per optical fiber) may suffer due to optical transmission and Polarization-related impairments suffer from severe yield loss, so more careful management of polarization-related impairments in optical transmission is required.

Embodiments described herein for mitigating and/or managing polarization-related impairments in optical transmission via PM optical data communication links may be used in optical systems having substantially any number of PM fibers optically connected to a particular integrated optical device. in the data communication system. Embodiments described herein for mitigating and/or managing polarization-related impairments in optical transmission over PM optical data communication links are particularly applicable to systems having four or more PM fibers attached to a single integrated optical device Optical data communication systems, even more applicable to optical data communication systems comprising nine or more optical fibers attached to a single integrated optical device, especially applicable to optical data communication systems comprising five or more optical fibers attached to a single integrated optical device A data communication system, wherein the single integrated optical device comprises one or more optical receiver elements/devices/parts/systems and/or one or more optical transmitter elements/devices/parts/systems.

Embodiments described herein for mitigating and/or managing polarization-related impairments in optical transmission over PM optical data communication links can be used in optical data communication systems having virtually any number of WDM wavelength channels per optical fiber middle. Embodiments described herein for mitigating and/or managing polarization-related impairments in optical transmission over PM optical data communication links are particularly applicable to optical data communication where each fiber comprises five or more WDM wavelength channels The system can even be applied to an optical data communication system in which each optical fiber contains eight or more WDM wavelength channels, and especially can be applied to an optical data communication system in which each optical fiber contains 12 or more WDM wavelength channels.

1 shows a diagram of an optical data communication system 100 comprising an optical transmitter 101 (Tx) optically connected to an optical receiver 105 (Rx) via a PM optical data communication link 103 according to some embodiments. The direction of travel of light traveling from optical transmitter 101 to optical receiver 105 via PM optical data communication link 103 is indicated by arrow 102 . The exemplary PM optical data communication link 103 includes five sections of PM optical fibers (plurality of optical fibers) 107-1, 107-2, 107-3, 107-4, 107-5. In certain embodiments, each section of PM fiber (plurality of fibers) 107-1, 107-2, 107-3, 107-4, 107-5 includes a plurality of fibers. In some embodiments, the plurality of fibers in each section of PM fibers 107-1, 107-2, 107-3, 107-4, 107-5 are collectively formed into an array of fibers such as a fiber optic ribbon. PM fiber segment 107 - 1 has a first end optically connected to the optical output of optical transmitter 101 . PM fiber segment 107-1 has a second end optically connected to optical connector 109-1. PM fiber segment 107-2 has a first end optically connected to optical connector 109-1 and a second end optically connected to optical connector 109-2. PM fiber segment 107-3 has a first end optically connected to optical connector 109-2 and a second end optically connected to optical connector 109-3. PM fiber segment 107-4 has a first end optically connected to optical connector 109-3 and a second end optically connected to optical connector 109-4. PM fiber segment 107 - 5 has a first end optically connected to optical connector 109 - 4 and a second end optically connected to the optical input of optical receiver 105 . In certain embodiments, the PM fiber segment 107-3 is longer than the other PM fiber segments 107-1, 107-2, 107-4, 107-5.

The optical data communication system 100 also includes a laser 111 for generating continuous wave laser light at one or more wavelengths and transmitting the continuous wave laser light to the optical transmitter 101 via the optical link 113 . Optical link 113 includes fiber optic sections 115-1, 115-2, and 115-3. Fiber segment 115 - 1 has a first end optically connected to the optical output of laser 111 . The fiber optic segment 115-1 has a second end optically connected to an optical connector 117-1. Fiber segment 115-2 has a first end optically connected to optical connector 117-1 and a second end optically connected to optical connector 117-2. Fiber segment 115 - 3 has a first end optically connected to optical connector 117 - 2 and a second end optically connected to the laser feed optical input of optical transmitter 101 . In some embodiments, each fiber section 115-1, 115-2, 115-3 is a single fiber. In certain embodiments, each fiber segment 115-1, 115-2, 115-3 includes a plurality of optical fibers. In some embodiments, each fiber segment 115-1, 115-2, 115-3 is formed of non-PM fiber (plurality of fiber). In these embodiments, the optical transmitter 101 (or an optical transceiver including the optical transmitter 101) is used to split the complex polarization of the incoming continuous wave laser light to be generated by the optical transmitter 101 for The modulated optical signal with a single polarization is transmitted via the PM optical data communication link 103 to the optical receiver 105 . In some embodiments, the laser 111 is configured to output continuous wave laser light (of one or more wavelengths) under a single polarization. In these embodiments, each fiber section 115-1, 115-2, 115-3 is formed of PM fiber (plurality of fiber).

In some embodiments, the optical transmitter 101 is implemented within an optical transceiver that includes both optical transmitter and optical receiver elements. Similarly, in some embodiments, the optical receiver 105 is implemented within an optical transceiver that includes both optical transmitter and optical receiver elements. In embodiments where the optical receiver 105 is implemented within an optical transceiver, the laser 111 is optically connected via an optical link 119 to the optical transceiver including the optical receiver 105 . Optical link 119 includes fiber optic sections 121-1, 121-2, and 121-3. The fiber section 121 - 1 has a first end optically connected to the optical output of the laser 111 . The fiber optic segment 121-1 has a second end optically connected to an optical connector 123-1. Fiber segment 121-2 has a first end optically connected to optical connector 123-1 and a second end optically connected to optical connector 123-2. Fiber segment 121 - 3 has a first end optically connected to optical connector 123 - 2 and a second end optically connected to a laser supply optical input of an optical transceiver comprising optical receiver 105 . In some embodiments, each fiber section 121-1, 121-2, 121-3 is a single fiber. In some embodiments, each fiber segment 121-1, 121-2, 121-3 includes a plurality of optical fibers. In some embodiments, each fiber section 121-1, 121-2, 121-3 is formed of non-PM fiber (plurality of fiber). In these embodiments, a transceiver including optical receiver 105 is used to split the complex polarizations of incoming continuous wave laser light to generate modulated optical signals having a single polarization. In some embodiments, the laser 111 is configured to output continuous wave laser light (of one or more wavelengths) under a single polarization. In these embodiments, each fiber section 121-1, 121-2, 121-3 is formed by PM fiber (plurality of fiber).

It should be appreciated that Figure 1 shows optical connections in a diagrammatic manner for ease of illustration. In some embodiments, however, in the actual implementation of the optical data communication system 100, the plurality of optical fibers carrying the optical link 113 of the laser light to the optical transmitter 101 is attached in a single array of optical fibers to the The integrated optics device of the transmitter 101 (integrated optical transceiver). Also, in some embodiments, in the actual implementation of the optical data communication system 100, the plurality of optical fibers of the PM optical data communication link 103 carrying the modulated optical signal leaving the optical transmitter 101 are separated by the plurality of optical fibers A single array is attached to an integrated optics device (integrated optical transceiver) including optical transmitters 101 . Also, in some embodiments, in the actual implementation of the optical data communication system 100, the plurality of optical fibers carrying the modulated optical signal into the PM optical data communication link 103 of the optical receiver 105 is a single optical fiber of the plurality of optical fibers. The array is attached to an integrated optics device (integrated optical transceiver) comprising optical receivers 105 .

In some embodiments, there is a small fiber-to-fiber misalignment at each of the optical connectors 109-1 , 109-2, 109-3, 109-4 within the PM optical data communication link 103 . Each fiber-to-fiber misalignment at optical connectors 109-1, 109-2, 109-3, 109-4 causes optical coupling between polarizations. Also, in some embodiments, each section of the PM optical fiber (plurality of optical fibers) 107-1, 107-2, 107-3, 107-4, 107-5 within the PM optical data communication link 103 causes deflection. The wavelength-dependent difference between the polarization phases. Also, in some embodiments, the optical coupling of each fiber to the wafer, such as between the optical transmitter 101 and a section of PM fiber (plural fiber) 107-1, such as between the optical receiver 105 and the PM fiber (plural fiber) ) The optical coupling between segments of 107-5 has the function of an optical polarization device.

In some embodiments, the polarization suppression device is optically coupled to the PM optical data communication link 103 . For example, FIG. 1 shows a first polarization suppression device 108-1 optically coupled to a first PM fiber 107-1 at a location between the optical output of the optical transmitter 101 and the first optical connector 109-1. Figure 1 also shows a second polarization suppressing device 108-2 optically coupled to a second PM optical fiber 107-2 at a location between the first optical connector 109-1 and the second optical connector 109-2. Figure 1 also shows a third polarization suppressing device 108-3 optically coupled to a third PM optical fiber 107-3 at a location between the second optical connector 109-2 and the third optical connector 109-3. Figure 1 also shows a fourth polarization suppressing device 108-4 optically coupled to a fourth PM optical fiber 107-4 at a location between the third optical connector 109-3 and the fourth optical connector 109-4. 1 also shows a fifth polarization suppression device 108-5 optically coupled to a fifth PM optical fiber 107-5 at a location between the fourth optical connector 109-4 and the optical input of the optical receiver 105. It should be appreciated that in various embodiments, the PM optical data communication link 103 may include a first polarization suppression device 108-1, a second polarization suppression device 108-2, a third polarization suppression device 108-3 , any one or more of the fourth polarization suppression device 108-4, and the fifth polarization suppression device 108-5. Also, in some embodiments, the PM optical data communication link 103 does not include the first polarization suppression device 108-1, the second polarization suppression device 108-2, and the third polarization suppression device 108-3 , any one of the fourth polarization suppression device 108-4, and the fifth polarization suppression device 108-5. In some embodiments, the first polarization suppression device 108-1, the second polarization suppression device 108-2, the third polarization suppression device 108-3, and the fourth polarization suppression device 108-4 , and any one or more of the fifth polarization suppression means 108-5 are polarization means for suppressing one of the two polarization modes. In some embodiments, the first polarization suppression device 108-1, the second polarization suppression device 108-2, the third polarization suppression device 108-3, and the fourth polarization suppression device 108-4 , and any one or more of the fifth polarization suppression means 108-5 are polarization-dependent loss elements for suppressing one of the two polarization modes.

FIG. 2 shows a self-500 Gigabit connection over a PM optical data communication link 103 comprising five PM fiber segments 107-1, 107-2, 107-3, 107-4, 107-5, according to certain embodiments. Various diagrams 201 , 202 , 203 , 204 of optical transmission in decibels (dB) over the frequency range Hertz (GHz) to +500 GHz. The different illustrations 201, 202, 203, 204 of light transmission shown in FIG. 2 correspond to the use of different lengths for the PM fiber section 107-3 (central PM fiber section) but the other PM fiber sections 107-1 , 107-2, 107-4, 107-5 are embodiments of PM optical data communication links 103 maintained at their respective length values. In each configuration used to produce the PM optical data communication link 103 shown in Figures 201, 202, 203, 204, the first PM fiber section 107-1 has a length of about 0.6 meters, the second PM fiber section 107-2 has a length of about 1 meter, the fourth PM fiber section 107-4 has a length of about 1 meter, and the fifth PM fiber section 107-5 has a length of about 0.6 meter. In the PM optical data communication link 103 used to generate the diagram 201, the third PM optical fiber section 107-3 has a length of about 3 meters. In the PM optical data communication link 103 used to generate the diagram 202, the third PM optical fiber section 107-3 has a length of about 10 meters. In the PM optical data communication link 103 used to generate the diagram 203, the third PM optical fiber section 107-3 has a length of about 30 meters. In the PM optical data communication link 103 used to generate the diagram 204, the third PM optical fiber section 107-3 has a length of about 100 meters.

To generate the graphs 201, 202, 203, 204, the fiber polarization mode dispersion (PMD) is approximately 1.3 picoseconds per meter (ps/m). The fiber PMD is the average differential group delay (DGD), where DGD is the time separation (or delay) between the two dominant polarization states at the optical receiver 105 . DGD is a random value that can be approximated by a Maxwell probability distribution. PMD is the average value of DGD over the distribution of a large number of independent DGD measurements. Each of the diagrams 201, 202, 203, 204 contains 16 random realizations drawn together. Also, in order to generate graphs 201, 202, 203, 204, the misalignment angles at 16 randomly implemented optical connectors 109-1, 109-2, 109-3, 109-4 are sampled to have a one-dimensional standard Poor independent Gaussian random variables.

A comparison of diagrams 201 , 202 , 203 , 204 shows that polarization coupling introduces frequency-dependent losses into the PM optical data communication link 103 . A comparison of graphs 201, 202, 203, 204 also shows that longer PM fibers produce rapid changes in optical transmission (due to increased PMD) with frequency, which is an undesired result. The worst-case optical loss across the wavelength range is a function of random misalignment at the optical connectors 109-1, 109-2, 109-3, 109-4 and can be determined by tightening the optical connectors 109-1, 109-1, Corner alignment margins at 109-2, 109-3, 109-4 reduce this optical loss. In certain embodiments, it is desirable to select a PM fiber with a relatively small PMD to produce a transmission response that oscillates less rapidly with frequency.

In some embodiments, the PM fiber segments 107-1, 107-2, 107-3, 107-4, 107- One or more of the optical connections between 5 (provided by optical connectors 109-1, 109-2, 109-3, 109-4). More specifically, for a particular pair of optically connected PM fibers, the slow axis of the PM fiber of one of the pair is aligned to the fast axis of the other PM fiber of the pair. This reversed alignment of the polarization axes at the junction between two PM fibers tends to introduce cancellation of the PMD of the two connected PM fibers and produces a less rapidly oscillating light transmission response with frequency.

3A shows a graph 301 of optical transmission (in dB) over the frequency range of PM optical data communication link 103 extending from -500 GHz to +500 GHz, according to some embodiments. PM fiber segments 107-1, 107-2, 107-3, 107-4, The fiber-to-fiber connection between 107-5 has a standard alignment of the polarization axis in which optical connectors 109-1, 109-2, 109-3, 109-4 The slow axis of one PM fiber of each connected pair of PM fibers is aligned to the slow axis of the other PM fiber. FIG. 3B shows a graph 302 of optical transmission (in dB) over the frequency range of PM optical data communication link 103 extending from -500 GHz to +500 GHz in accordance with certain embodiments. PM fiber segments 107-1, 107-2, 107-3, 107-4, The fiber-to-fiber connection between 107-5 has an upside-down alignment of the polarization axis (connection of alternate orientations of the polarization axis of the PM fiber), in the upside-down alignment of the polarization axis in the optical connector 109 - The slow axis of one PM fiber of each connected pair of PM fibers at 1, 109-2, 109-3, 109-4 is aligned to the fast axis of the other PM fiber. After being used to produce the PM optical data communication link 103 shown in Figures 301 and 302, the first PM fiber section 107-1 has a length of about 0.2 meters, and the second PM fiber section 107-2 has a length of about 5 meters , the third PM fiber section 107-3 has a length of about 10 meters, the fourth PM fiber section 107-4 has a length of about 5 meters, and the fifth PM fiber section 107-5 has a length of about 0.2 meters. A comparison of graphs 301 and 302 shows that a PM fiber connection using an inverted alignment of the polarization axis (graph 302 ) yields a substantially smoother frequency response and relatively average and minimal light transmission.

In some embodiments, one or more polarization devices and/or polarization-dependent loss elements are inserted within the PM optical data communication link 103 such that even optical connectors 109-1, 109-2 , 109-3, 109-4 at one or more of PM fiber sections 107-1, 107-2, 107-3, 107-4, 107-5 misalignment between PM fibers within the PM fiber section (plural Misalignment) produces unfavorable polarization components, and can also eliminate unfavorable polarization components before they are coupled back into the main polarization. 4A shows the extension from -500 GHz at PM optical data communication link 103 comprising five PM fiber segments 107-1, 107-2, 107-3, 107-4, 107-5, according to some embodiments. Diagram 401 of optical transmission (in dB) over the frequency range to +500 GHz, PM optical data communication link 103 with polarization means inserted. In the PM optical data communication link 103 used to generate diagrams 401 and 402, the first PM fiber section 107-1 has a length of about 0.4 meters, and the second PM fiber section 107-2 has a length of about 1.2 meters , the third PM fiber section 107-3 has a length of about 5 meters, the fourth PM fiber section 107-4 has a length of about 1.2 meters, and the fifth PM fiber section 107-5 has a length of about 0.4 meters. Each of diagrams 401 and 402 contains 100 random realizations drawn together. Also, to generate graphs 401 and 402, the fiber misalignment angles were sampled for 100 randomly implemented fibers at optical connectors 109-1, 109-2, 109-3, 109-4 to have a one-dimensional standard deviation independent Gaussian random variables. The diagram 401 of Fig. 4 A is for the PM optical data communication link 103 without a polarization device inserted, and the diagram 402 of Fig. Each of 107-4, 107-5 has a polarization device (complex number of polarization devices) inserted in each of the five PM fiber sections 107-1, 107-2, 107-3, 107-4, 107 PM optical data communication link 103 providing 6 dB undesired polarization suppression in each of -5. A comparison of diagrams 401 and 402 shows that the insertion of polarization devices within the PM optical data communication link 103 can substantially reduce optical transmission loss.

FIG. 5A shows the 3.4 terahertz (THz) frequency range in the configuration of PM optical data communication link 103 used to generate graphs 401 and 402 of FIGS. 4A and 4B , respectively, which is an example of a WDM system, according to certain embodiments. Graphs 501 and 502 of the cumulative distribution functions (estimated from 1024 realizations) of the worst optical transmission loss over the entire range of performance) for 1024 random realizations of optical connectors 109-1, 109-2, 109- 3. The optical fiber at 109-4 samples the misalignment angle of the optical fiber to become an independent Gaussian random variable with a one-dimensional standard deviation. For a particular level of polarization-dependent impairments, the PM optical data communication link 103 (shown 502 ) with a polarization device is more efficient than the PM optical data communication link (shown 501 ) without a polarization device. ) has a much higher cumulative probability. Thus, a PM optical data communication link 103 with a polarization device is far less likely to screw up the desired level of performance. For example, if the optical data communication system 100 requires a worst-case optical transmission loss of less than or equal to 0.15 dB within the 3.4 THz operating frequency band, the PM optical data communication link 103 without polarization devices has a probability of about 5 percent The worst optical transmission loss requirement is messed up, but the PM optical data communication link 103 with polarization devices has a probability of worst optical transmission loss requirement well below 1 percent.

5B shows the worst-case optical transmission loss over the 3.4 terahertz (THz) frequency range for the PM optical data communication link 103 configuration used to generate graphs 401 and 402 of FIGS. 4A and 4B , respectively, according to certain embodiments. Plots 503 and 504 of the cumulative distribution function (estimated from 1024 implementations) for fiber-to-fiber losses at 1024 randomly implemented optical connectors 109-1, 109-2, 109-3, 109-4 The quasi-angles are sampled as independent Gaussian random variables with two-dimensional standard deviations. For a particular level of polarization-dependent impairments, the PM optical data communication link 103 (shown 504 ) with a polarization device is more efficient than the PM optical data communication link (shown 503 ) without a polarization device. ) has a much higher cumulative probability. Thus, PM optical data communication links 103 containing polarization devices are far less likely to fall short of the desired level of performance. Two standard deviation Gaussian samples of the fiber-to-fiber misalignment angles at the optical connectors 109-1, 109-2, 109-3, 109-4 represent that the optical connectors are matched to the ribbon and array. Under standard assumptions, as shown in diagram 503, worst-case optical transmission losses greater than about 1 dB are rarely seen, but still occur in one to two percent of optical links. If the integrating optics device is attached to an array of optical fibers forming a number (N, such as N=4) of optical links, the yield loss is approximately N times the yield of each link. In this case, a failure rate of one to two percent per optical link may not be acceptable.

The impact of polarization-related impairments on the overall performance (such as capacity, bit error rate, power consumption, etc.) of an optical data communication system will depend on the signal processing technology used. Such signal processing techniques may include analog or digital techniques. Also, in some embodiments, such signal processing techniques are implemented in circuits. In some embodiments, the receive integrated optics device includes on-chip circuitry to perform continuous-time linear equalization (CTLE) or other types of linear equalization. In some embodiments, the receive integrated optics device includes on-chip circuitry to perform decision feedback equalization (DFE) or other types of nonlinear equalization. In some embodiments using a DFE, reducing the PMD makes the time domain representation of polarization-dependent impairments fall within the range of samples available in the DFE.

In some embodiments, the length of the fiber is customized to improve the likelihood of having a low polarization-loss optical link. For example, when an application requires the desired range, there is substantial freedom in choosing the length of the individual fiber segments within the optical link. In certain embodiments, certain techniques are implemented to achieve better angular margins and/or less cross-coupling between connected PM fiber segments, including but not limited to selecting optical connections with better margins Such as single fiber connectors (eg, especially Fixed Connection (FC) connectors), fiber optic array connectors (eg, especially Mechanical Transfer (MT) connectors), or other types of optical connectors. Also, in some embodiments, 25 spliced individual fibers or spliced fiber ribbons are used to achieve better angular margin and/or less cross-coupling between connected PM fiber segments.

In certain embodiments, the optical fiber(s) are optically connected to the integrated optics device using a connector for optical alignment and/or testing purposes and to achieve better polarization performance in final operation. In certain embodiments, a sacrificial connector is attached to an integrated optics device or coupling assembly to provide optical alignment and/or testing, where the sacrificial connector is removed at a later time. In some embodiments, the fiber optic array is attached to an integrated optics device. In such embodiments, the fiber array includes a subset of fibers for optical alignment and/or testing that is fanned out and connected from other fibers.

The simulations used to generate the graphs shown in Figures 2, 3A, 3B, 4A, 4B, 5A, and 5B are represented using Jones matrices, where the polarization of the input signal is represented by a two-dimensional complex vector u _in . A 2x2 matrix represents each conversion of polarization eg by the n ^th section of fiber ( T _n ^fiber ) or the m ^th coupling point ( T _m ^c ), and by cascading these conversions in the following way And calculate the output polarization: U _out = T _N+1 ^c T _N ^fiber … T ₂ ^fiber T ₂ ^c T ₁ ^fiber T ₁ ^c u _in

Each segment of the PM fiber in a multi-segment PM optical data communication link such as 103 imparts a frequency dependence between the primary polarization (which ideally should be excited) and the secondary undesired polarization The difference phase Φ _n ( f ). Commercially available PMFs have beat lengths on the order of millimeters (mm), so for reasonable fiber lengths much longer than one centimeter (cm), the difference is enormous. Also, the uncertainty of fiber length caused by cutting accuracy even has the level of beat frequency length. Therefore, it is assumed that each section of optical fiber within a multi-section PM optical data communication link randomly rephases the phase polarization components. Also, the frequency-dependent differential phase is typically characterized by PMD delay (on the order of 1 picosecond per meter PMF) and can be adjusted by fiber design and/or selection.

Every time light passes through a PMF section in a PM optical link and is coupled incompletely, the interference between the two delayed components becomes locked and can cause a breakdown at the optical receiver. In some embodiments, the optical coupling between PM segments or devices is characterized by the extinction ratio or the (effective) misalignment angle θ, which is defined for ideal emission such that the coupling The power in the desired and undesired polarizations is proportional to cos ² (θ) and sin ² (θ) respectively, and the extinction ratio (ER) is defined as ER = −10 log 10( tan ² (θ)) . This is discussed in "Application Note – Polarization Measurements – OZ Optics Family of Polarization Maintaining Components, Sources, and Measurements Systems," OZ Optics LTD., Canada, August 6, 1999, the entire contents of which are incorporated herein for all purposes for reference.

According to the foregoing, in some embodiments, the disclosed optical data communication system (such as 100) includes an optical transmitter (such as 101), an optical receiver (such as 105), and an optical output extending from the optical transmitter to PM optical data communication link (eg 103 ) for the optical input of the optical receiver. In certain embodiments, an optical transmitter is used to transmit modulated light having a plurality of WDM wavelengths over a PM optical data communication link. The PM optical data communication link comprises at least two sections (eg 107-1 to 107-5) of PM optical fiber optically connected via optical connectors (eg 109-1 to 109-4). In some embodiments, at least two sections of the PM fiber have different lengths. In some embodiments, the length of at least one of the at least two sections of the PM fiber is at least three times greater than the length of the other of the at least two sections of the PM fiber. In certain embodiments, each of at least two sections of PM fiber comprises a plurality of PM fibers. In some of these embodiments, the plurality of PM fibers is formed from a fiber ribbon.

In some embodiments, optical connectors (such as 109-1 to 109-4) are used to optically align the fast polarization axis of the first PM fiber to the slow polarization axis of the second PM fiber and enable The slow polarization axis of the first PM fiber is optically aligned to the fast polarization axis of the second PM fiber. In certain embodiments, one or more of the at least two sections of the PM fiber include polarization means (eg, 108-1 to 108-5) to suppress one of two polarization modes. In certain embodiments, each of at least two sections of the PM fiber includes separate polarization means to suppress the same of the two polarization modes. In some embodiments, one or more of at least two sections of the PM fiber include polarization-dependent loss elements (e.g., 108-1 to 108-5) to suppress one of the two polarization modes. ).

In some embodiments, the PM optical data communication link (such as 103) includes at least two optical connectors (such as 109-1 to 109-4), wherein each of the at least two optical connectors is optically connected to a Separate the PM fiber of the pair (such as 107-1 to 107-5) so that the fast polarization axis system of the first polarization maintaining fiber of the split pair of polarization maintaining fiber is connected to the polarization maintaining fiber of the split pair The second polarization maintains the substantial alignment of the slow polarization axis of the fiber. In certain embodiments, when the fiber-to-fiber misalignment angle is less than or equal to about 10 degrees, the fast polarization axis of the first PM fiber connected between the first and second PM fibers is aligned with the second PM fiber. The slow polarization axes of the fibers are substantially aligned. The fiber-to-fiber misalignment angle is defined as the first PM measured along the optical core centerline of the first PM fiber or the second PM fiber when the optical core centerlines of the first and second PM fibers are aligned with each other. The angle between the fast polarization axis of the fiber and the slow polarization axis of the second PM fiber. In certain embodiments, when the fiber-to-fiber misalignment angle is less than or equal to about 6 degrees, the fast polarization axis of the first PM fiber connected between the first and second PM fibers is aligned with the second PM fiber. The slow polarization axes of the fibers are substantially aligned. In certain embodiments, when the fiber-to-fiber misalignment angle is less than or equal to about 3 degrees, the fast polarization axis of the first PM fiber connected between the first and second PM fibers is aligned with the second PM fiber. The slow polarization axes of the fibers are substantially aligned.

In some embodiments, the PM optical data communication link (such as 103) includes a first optical connector (such as 109-1), a second optical connector (such as 109-2), a third optical connector (such as 109 -3), the fourth optical connector (such as 109-4), optically connected to the first PM optical fiber (such as 107-1) between the output of the optical transmitter (such as 101) and the first optical connector, optical connection The second PM optical fiber (such as 107-2) between the first optical connector and the second optical connector, the third PM optical fiber (such as 107-2) optically connected between the second optical connector and the third optical connector -3), the fourth PM optical fiber (such as 107-4) optically connected between the third optical connector and the fourth optical connector, and the optical connection between the fourth optical connector and the optical receiver (such as 105) Fifth PM fiber (eg 107-5) between optical inputs. In some embodiments, the first optical connector is used to align the fast polarization axis of the first PM fiber to the slow polarization axis of the second PM fiber, and to align the slow polarization axis of the first PM fiber The polarization axis is aligned to the fast polarization axis of the second PM fiber. Also, the second optical connector is used to align the fast polarization axis of the second PM fiber to the slow polarization axis of the third PM fiber, and to align the slow polarization axis of the second PM fiber to the The fast polarization axis of the third PM fiber. Also, the third optical connector is used to align the fast polarization axis of the third PM fiber to the slow polarization axis of the fourth PM fiber, and to align the slow polarization axis of the third PM fiber to the The fast polarization axis of the fourth PM fiber. Also, the fourth optical connector is used to align the fast polarization axis of the fourth PM fiber to the slow polarization axis of the fifth PM fiber, and to align the slow polarization axis of the fourth PM fiber to the The fast polarization axis of the fifth PM fiber.

In some embodiments, the first polarization suppressing device (eg, 108-1) is optically coupled to the first optical connector (eg, 109-1) between the optical output of the optical transmitter (eg, 101) and the first optical connector (eg, 109-1). The first PM fiber at position (such as 107-1). Also, the second polarization suppressing device (such as 108-2) is optically coupled to the first optical connector (such as 109-1) and the second optical connector (such as 109-2) at a position between Two PM fibers (such as 107-2). Also, a third polarization suppressing device (such as 108-3) is optically coupled to the first optical connector at a position between the second optical connector (such as 109-2) and the third optical connector (such as 109-3). Three PM fibers (such as 107-3). Also, a fourth polarization suppressing device (such as 108-4) is optically coupled to the first optical connector at a position between the third optical connector (such as 109-3) and the fourth optical connector (such as 109-4). Four PM fibers (such as 107-4). Also, a fifth polarization suppressing device (such as 108-5) is optically coupled to the fifth optical connector (such as 109-4) at a position between the optical input of the optical receiver (such as 105). PM fiber (such as 107-5).

In addition, according to the foregoing, in some embodiments, the disclosed optical data communication system (such as 100) includes a PM optical data communication link (such as 103), and the PM optical data communication link (such as 103) includes an optically coupled to The first PM fiber (such as any of 107-1 to 107-5) of the second PM fiber (such as any other of 107-1 to 107-5) such that the fast polarization axis of the first PM fiber is aligned with the slow polarization axis of the second PM fiber and the slow polarization axis of the first PM fiber is aligned with the fast polarization axis of the second PM fiber. In some embodiments, a polarization suppressing device (such as any of 108-1 to 108-5) is optically coupled to the PM optical data communication link. In certain embodiments, each optical connection between any two PM fibers within a PM optical data communication link has the fast polarization of one PM fiber aligned with the slow polarization axis of the other PM fiber axis. In some embodiments, a PM optical data communication link extends from an optical output of an optical transmitter (eg, 101 ) to an optical input of an optical receiver (eg, 105 ).

Figure 6 shows an outline of a method of operating an optical data communication system according to some embodiments. The method of FIG. 6 includes operation 601 of transmitting a complex optical signal from an output of an optical transmitter (eg 101 ) to an optical input of an optical receiver (eg 105 ) via a PM optical data communication link (eg 103 ). The PM optical data communication link comprises at least two sections of PM optical fibers (eg 107-1 to 107-5) optically connected via optical connectors (eg 109-1 to 109-4). The at least two sections of the PM fiber have different lengths. In some embodiments, the method of FIG. 6 also includes operation 603, optically aligning the fast polarization axis of the first PM fiber of the at least two sections of the PM fiber to the at least two sections of the PM fiber The slow polarization axis of the second PM fiber. In some embodiments, the method of FIG. 6 also includes operation 605 of optically coupling polarization suppression devices (eg, 108-1 to 108-5) to optical fibers within the at least two sections of the PM optical fiber.

Figure 7 shows an outline of a method of operating an optical data communication system according to some embodiments. The method of FIG. 7 includes operation 701, transmitting a plurality of optical signals through a first PM optical fiber (such as any one of 107-1 to 107-5), the PM optical data communication link (such as 103) comprising optically coupling to a second PM The first PM fiber (such as any one of 107-1 to 107-5) of the optical fiber (such as any other of 107-1 to 107-5) such that the fast polarization axis of the first PM fiber is aligned with The slow polarization axis of the second PM fiber is aligned and the slow polarization axis of the first PM fiber is aligned with the fast polarization axis of the second PM fiber. In some embodiments, the method of FIG. 7 includes an operation 703 of optically coupling polarization suppression devices (eg, 108-1 to 108-5) to the PM optical data communication link. In some embodiments, a PM optical data communication link optically connects an optical output of an optical transmitter (eg, 101 ) to an optical input of an optical receiver (eg, 105 ).

The description of the foregoing embodiments is provided for purposes of illustration and description, and it is not intended to exclude other possibilities or limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable, which can be used in a selected embodiment, even if not specifically shown or described herein. In this way, one or more features from one or more embodiments herein may be combined with one or more features from one or more other embodiments herein to form another embodiment that is not explicitly disclosed but may be considered implicitly disclosed. Example. This other embodiment can also be varied in many ways. Such embodiment changes should not be regarded as departing from the disclosure content of the present invention, and all such embodiment changes and modifications should be included in the disclosure scope of the present invention.

Although certain method operations are described herein in a particular order, it should be understood that other idle operations may be performed between method operations or may be adjusted to occur so long as the processing of the method operations can be performed in a manner that enables the successful implementation of the method. At slightly different times or at the same time, or method operations can be distributed into systems that allow method operations to be performed at various intervals.

Although the foregoing embodiments have been described in detail in order to enable those skilled in the art to clearly understand the invention, it should be understood that certain changes and modifications may be made within the scope of the appended claims. Accordingly, such embodiments should be regarded as illustrative rather than restrictive, and embodiments are not limited to the details set forth herein, modifications may be made within the scope and equivalents of the appended claims.

100:Optical data communication system 101, 101(Tx): optical transmitter 102: Arrow 103: PM optical data communication link 105, 105(Rx): optical receiver 107-1, 107-2, 107-3, 107-4, 107-5: PM fiber section 108-1: The first polarization suppression device 108-2: Second polarization suppression device 108-3: The third polarization suppression device 108-4: The fourth polarization suppression device 108-5: Fifth polarization suppression device 109-1, 109-2, 109-3, 109-4: Optical connectors 111:Laser 113: Optical link 115-1, 115-2, 115-3: fiber optic section 117-1, 117-2: Optical connectors 119: Optical link 121-1, 121-2, 121-3: fiber optic section 123-1, 123-2: Optical connectors 201, 202, 203, 204: icon 401, 402: icon 501, 502, 503, 504: icon 601, 603, 605: operation 701, 703: operation

Figure 1 shows a diagram of an optical data communication system comprising an optical transmitter optically connected to an optical receiver via a polarization maintaining optical data communication link, according to some embodiments.

2 shows various diagrams of light transmission over the frequency range of the polarization maintaining optical data communication link of FIG. 1, according to some embodiments.

3A shows a diagram of light transmission over the frequency range of the polarization-maintaining optical data communication link of FIG. 1 , in accordance with some embodiments, in which Polarization at each optical connector maintains fiber-to-fiber connections between fiber segments with standard alignment of polarization axes.

3B shows a graphical representation of light transmission over the frequency range of the polarization-maintaining optical data communication link of FIG. Polarization at each optical connector maintains fiber-to-fiber connections between fiber segments with an inverted alignment of polarization axes.

4A shows a diagram of light transmission over the frequency range of the polarization-maintaining optical data communication link of FIG. Polarization device.

4B shows a graphical representation of light transmission over the frequency range of the polarization-maintaining optical data communication link of FIG. 1 in which the polarization-maintaining optical data communication link of FIG. Polarization device.

5A shows a graphical representation of the cumulative distribution function of worst-case optical transmission loss over the frequency range for the configuration of the polarization-maintaining optical data communication link of FIG. 1 , according to certain embodiments. The configuration of the optical data communication link was used to generate the graphs of Figures 4A and 4B, respectively, in which the fiber-to-fiber misalignment angles at the optical connectors were sampled as independent Gaussian random variables with one-dimensional standard deviations.

5B shows a graphical representation of the cumulative distribution function of worst-case optical transmission loss over the frequency range for the configuration of the polarization-maintaining optical data communication link of FIG. 1 , according to certain embodiments. The configuration of the optical data communication link was used to generate the graphs of Figures 4A and 4B, respectively, in which the fiber-to-fiber misalignment angles at the optical connectors were sampled as independent Gaussian random variables with two-dimensional standard deviations.

Figure 6 shows an outline of a method of operating an optical data communication system according to some embodiments.

Figure 7 shows an outline of a method of operating an optical data communication system according to some embodiments.

100:Optical data communication system

101, 101(Tx): optical transmitter

102: Arrow

103: PM optical data communication link

105, 105(Rx): optical receiver

107-1, 107-2, 107-3, 107-4, 107-5: PM fiber section

108-1: The first polarization suppression device

108-2: Second polarization suppression device

108-3: The third polarization suppression device

108-4: The fourth polarization suppression device

108-5: Fifth polarization suppression device

109-1, 109-2, 109-3, 109-4: Optical connectors

111:Laser

113: Optical link

115-1, 115-2, 115-3: fiber optic section

117-1, 117-2: Optical connectors

119: Optical link

121-1, 121-2, 121-3: fiber optic section

123-1, 123-2: Optical connectors

Claims (20)

An optical data communication system comprising: an optical transmitter; an optical receiver; and A polarization maintaining optical data communication link extending from an optical output of the optical transmitter to an optical input of the optical receiver, the polarization maintaining optical data communication link comprising optical connection via an optical connector At least two sections of the polarization maintaining fiber have different lengths. The optical data communication system as claimed in claim 1, wherein the optical connector is used to optically align a fast polarization axis of a first polarization maintaining optical fiber with a slow polarization of a second polarization maintaining optical fiber A polarization axis, wherein the optical connector is used to align a slow polarization axis of the first polarization maintaining optical fiber with a fast polarization axis of the second polarization maintaining optical fiber. The optical data communication system of claim 1, wherein one or more of the at least two sections of the polarization maintaining optical fiber includes a polarization device for suppressing one of two polarization modes. The optical data communication system of claim 1, wherein each of the at least two sections of the polarization maintaining optical fiber includes a separate polarization device for suppressing the same one of the two polarization modes. The optical data communication system of claim 1, wherein one or more of the at least two sections of the polarization maintaining optical fiber include a polarization-dependent loss for suppressing one of two polarization modes element. The optical data communication system according to claim 1, wherein the length of at least one section of the at least two sections of the polarization maintaining optical fiber is longer than the other section of the at least two sections of the polarization maintaining optical fiber One of the segments is at least three times as long. The optical data communication system according to claim 1, wherein each of the at least two sections of the polarization maintaining optical fiber comprises a plurality of polarization maintaining optical fibers. The optical data communication system as claimed in claim 7, wherein the plurality of polarization maintaining optical fibers is formed as an optical fiber ribbon. The optical data communication system according to claim 1, wherein the optical transmitter is used for transmitting modulated light having multiple wavelengths of wavelength division multiplexing through the polarization maintaining optical data communication link. The optical data communication system of claim 1, wherein the polarization maintaining optical data communication link comprises at least two optical connectors, wherein each of the at least two optical connectors is optically connected to a split pair of polarities polarization maintaining fiber such that the fast polarization axis of the first polarization maintaining fiber of the split pair is substantially aligned with the first polarization maintaining fiber of the split pair Dual polarization maintains one of the slow polarization axes of the fiber. An optical data communication system comprising: A polarization maintaining optical data communication link comprising a first polarization maintaining fiber optically coupled to a second polarization maintaining fiber such that a fast polarization axis of the first polarization maintaining fiber is aligned with one of the slow polarization axes of the second polarization maintaining fiber and such that one of the slow polarization axes of the first polarization maintaining fiber is aligned with one of the second polarization maintaining fibers Fast polarizing axis. The optical data communication system as claimed in item 11 further includes: A polarization suppressing device is optically coupled to the polarization maintaining optical data communication link. The optical data communication system as claimed in claim 11, wherein each optical connection between any two polarization maintaining optical fibers in the polarization maintaining optical data communication link has a fast polarization of a polarization maintaining optical fiber The polarization axis is aligned with one of the slow polarization axes of the other polarization maintaining fiber. The optical data communication system as claimed in item 11 further includes: an optical transmitter; and An optical receiver, the polarization maintaining optical data communication link extends from an optical output of the optical transmitter to an optical input of the optical receiver. A method of operating an optical data communication system, comprising: Transmitting a plurality of optical signals from an output of an optical transmitter to an optical input of an optical receiver via a polarization maintaining optical data communication link comprising via an optical connector The at least two sections of the polarization maintaining optical fiber of the optical connection have different lengths. For example, the operation method of the optical data communication system in claim 15 further includes: optically aligning a fast polarization axis of the first polarization maintaining fiber of the at least two sections of the polarization maintaining fiber to a second polarization axis of the at least two sections of the polarization maintaining fiber Polarization maintains one of the slow polarization axes of the fiber. For example, the operation method of the optical data communication system in claim 15 further includes: A polarization suppressing device is optically coupled to an optical fiber within the at least two sections of the polarization maintaining optical fiber. A method of operating an optical data communication system, comprising: Transmitting a plurality of optical signals via a polarization maintaining optical data communication link such that a fast polarization axis of a first polarization maintaining fiber and a slow polarization axis of a second polarization maintaining fiber aligned so that a slow polarization axis of the first polarization maintaining optical fiber is aligned with a fast polarization axis of the second polarization maintaining optical fiber, the polarization maintaining optical data communication link A circuit includes the first polarization maintaining fiber optically coupled to the second polarization maintaining fiber. For example, the operation method of the optical data communication system in claim item 18 further includes: A polarization suppressing device is optically coupled to the polarization maintaining optical data communication link. The method of operating an optical data communication system according to claim 18, wherein the polarization maintaining optical data communication link optically connects an optical output of an optical transmitter to an optical input of an optical receiver.

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